It could be argued that because of his character, Serpico cannot do anything but expose corruption. All of his life Serpico wanted to become a police officer for noble reasons. It because of his ethics and his humanity off the job (he loves dancing and dogs) officers like Green do not understand him. The job scars Serpico, and embitters him, supporting a deontological view of the world that suggests without ethics the souls of those who uphold the laws become too damaged to really do an effective job. The corrupt officers like Green do not care even when a suspected cop killer may go free, what they care about is getting extra money, and as much as possible. The rationalization of utilitarianism ultimately results in 'looking out for number one' rather than the 'greatest good' for the 'greatest number. The question arises as to what 'greatest good' and 'greatest number' the utilitarian is...

One cannot be ethical in the hopes of getting a reward like the corrupt get rewards through payoffs. Serpico is abandoned and shot by a drug dealer, deliberately by his partners -- so much for the blue wall of loyalty. Serpico survives and goes 'public' by testifying to a public commission on police corruption, but the life that he dreamt of on the police force has ended by virtue of exposing what he has seen. By striving to become the best and most ethical police officer possible, he is denied that chance, yet for the deontological ethicist, virtue must be its own reward.
Works Cited

Serpico. Directed by Sidney Lumet 1973.